Thermal Cell

ABSTRACT

An energy storage apparatus comprising: a casing; at least one crucible ( 150 ); at least one heating element adjacent the crucible ( 130 ); at least one heat conduit, having an inlet and outlet, adjacent the crucible ( 140 ); and a phase change material located within the at least one crucible, the phase change material selected from the group consisting of aluminium-silicon alloys, aluminium, magnesium chloride, sodium chloride and potassium chloride.

FIELD OF THE INVENTION

The present invention relates to the field of energy storage. Moreparticularly, the invention relates to an apparatus and method forstoring energy. Most particularly, the invention relates to an energystorage apparatus.

BACKGROUND TO THE INVENTION

Any reference to background art herein is not to be construed as anadmission that such art constitutes common general knowledge inAustralia or elsewhere.

Today's population relies heavily on electricity and its use, andtherefore demand on a network can vary considerably according to theseason and even to different times of the day. Energy storage systemscan be used to improve the performance of energy systems by levellingout the supply of electricity and increasing the reliability of thesystem at peak times. For example, energy storage systems can improvethe performance of a power generating plant by load levelling. Loadlevelling is a method for reducing energy fluctuations in customerdemand by storing energy when there is little demand for electricity,and releasing this stored energy when there is a spike in demand.Further to this, load levelling also improves the cost effectiveness ofa power generating plant.

The sun provides an abundance of clean and safe energy. However, thesupply of solar energy is periodic following yearly and diurnal cycles,and can be unpredictable. The energy demand of the population is alsounsteady, and follows a yearly and diurnal cycle for both industrial andresidential needs. The use of energy storage systems can help alleviatethe problem of this unpredictability by storing energy when there is anabundance of solar energy, and releasing it when there is a drop insupply. Further to this, energy storage is also useful when there is abreak in the supply of electricity, such as in a blackout.

Typically batteries are used to store energy but their cost andreplacement become an overriding factor when energy demand is 5 kW orgreater. One important characteristic of an energy storage system is thelength of time which energy can be stored with acceptable losses. Onedisadvantage of storing energy in the form of thermal energy is that itcan only be stored for short timeframes due to the loss of thermalenergy through radiation, convection and conduction. It would bedesirable to have an energy storage system that alleviates the problemsassociated with thermal energy loss.

Another important characteristic of an energy storage system is itsvolumetric energy capacity, or the amount of energy stored per unitvolume. If the energy required to be stored is large then the energystorage system will also be large. A large energy storage unit isundesirable due to transport and storage issues. As such, it isdesirable to have an energy storage apparatus that is more compact.

Heat storage at power generating plants is typically in the form ofsteam or hot water and can only be stored for short periods of time.Recently, other materials such as oils, that have a high boiling point,have been suggested as heat storage substances. However, these heatstorage substances lose thermal energy to the surroundings quickly.Another problem with the prior art thermal energy storage systems is thedesign of the heat exchangers which result in a substantial amount ofheat, and hence energy, being lost to the surroundings.

It should apparent to those skilled in the art that there is need for anenergy storage apparatus that is able to store large amounts of energywithout losing a substantial amount of energy, and is relativelycompact.

SUMMARY OF THE INVENTION

In a first aspect, although it need not be the only or indeed thebroadest form, the invention resides in an energy storage apparatuscomprising:

a casing;

at least one crucible;

at least one heating element adjacent the crucible;

at least one heat conduit, having an inlet and outlet, adjacent thecrucible; and

a phase change material located within the at least one crucible, thephase change material selected from the group consisting ofaluminium-silicon alloys, aluminium, magnesium chloride, sodium chlorideand potassium chloride.

In one embodiment, the phase change material is an aluminium-siliconalloy.

In another embodiment, the aluminium-silicon alloy comprises betweenabout 1% and 30% by weight of aluminium.

In an embodiment, the phase change material is AlSi₁₂.

In another embodiment, the phase change material is AlSi₂₀.

In one embodiment, the crucible is formed from a material selected fromsilicon carbide, graphite, reinforced polymer, clay, porcelain,ceramics, carbon nanotubes, aluminium nitride, aluminium oxide, boronnitride, silicon nitride or a combination thereof.

In another embodiment, the energy storage apparatus further comprises athermal interface between the casing and the crucible.

In a further embodiment, the thermal interface is selected from thegroup consisting of graphite, graphene and carbon nanotubes.

In an embodiment, the energy storage apparatus further comprisesinsulation.

In a second aspect, the invention resides in a method of storing andretrieving energy comprising the steps of:

-   -   a. providing an energy storage apparatus comprising:

a casing

at least one crucible;

at least one heating element adjacent the crucible;

at least one heat conduit, having an inlet and outlet, adjacent thecrucible; and

a phase change material located within the at least one crucible, thephase change material selected from the group consisting ofaluminium-silicon alloys, aluminium, magnesium chloride, sodium chlorideand potassium chloride;

-   -   b. heating the at least one heating element to cause a phase        change in the phase change material, to thereby store energy;    -   c. introducing a liquid to the at least one heat conduit; and    -   d. converting the liquid to a gas through absorption of thermal        energy stored in the phase change material;        -   to thereby retrieve stored energy.

The various features and embodiments of the present invention referredto in the individual sections above apply, as appropriate, to othersections, mutatis mutandis. Consequently features specified in onesection may be combined with features specified in other sections asappropriate.

Further features and advantages of the present invention will becomeapparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

To assist in understanding the invention and to enable a person skilledin the art to put the invention into practical effect, preferredembodiments of the invention will be described by way of example onlywith reference to the accompanying drawings, in which:

FIG. 1 shows a sectional view of an embodiment of the energy storageapparatus;

FIG. 1a shows a section view of another embodiment of the energy storageapparatus;

FIG. 2 shows a perspective sectional view of the energy storageapparatus;

FIG. 2a shows a perspective view of another embodiment of the energystorage apparatus;

FIG. 2b shows a view of the thermal interface of FIG. 2a where thecrucible is partially removed; and

FIG. 3 shows a graphical representation of the storage capacity per unitmass of AlSi₁₂ vs temperature.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention reside primarily in an energystorage apparatus. Accordingly, the method steps and apparatus have beenillustrated in concise schematic form in the drawings, showing onlythose specific details that are necessary for understanding theembodiments of the present invention, but so as not to obscure thedisclosure with excessive detail that will be readily apparent to thoseof ordinary skill in the art having the benefit of the presentdescription.

In this specification, adjectives such as first, second, adjacent andthe like may be used solely to distinguish one element or action fromanother element or action without necessarily requiring or implying anyactual such relationship or order. Words such as “comprises” or“includes” are intended to define a non-exclusive inclusion, such that amethod or apparatus that comprises a list of elements do not includeonly those elements but may include other elements not expressly listed,including elements that are inherent to such a process, method, article,or apparatus.

As used herein, the term ‘about’ means the amount is nominally thenumber following the term ‘about’ but the actual amount may vary fromthis precise number to an unimportant degree.

In a first aspect, although it need not be the only or indeed thebroadest form, the invention resides in an energy storage apparatuscomprising:

a casing;

at least one crucible;

at least one heating element adjacent the crucible;

at least one heat conduit, having an inlet and outlet, adjacent thecrucible; and

a phase change material located within the at least one crucible, thephase change material selected from the group consisting ofaluminium-silicon alloys, aluminium, magnesium chloride, sodium chlorideand potassium chloride.

Referring to FIG. 1 there is shown an energy storage apparatus 100. Theenergy storage apparatus 100 comprises a casing 110, a crucible 120, aheating element 130, a heat conduit 140, a phase change material 150, athermal interface 160 and insulation 170.

The crucible 120, the heating element 130, the heat conduit 140, thephase change material 150, the thermal interface 160 and insulation 170are encased within the casing 110. The phase change material 150 islocated within the crucible 120 such that when the crucible 120 isheated, the thermal energy is transferred to the phase change material150. The phase change material 150 is heated to high temperatures so itwill be appreciated that the crucible 120 has high mechanicalproperties, high thermal conductivity and is stable at hightemperatures. This allows the crucible 120 to facilitate thermal energytransfer whilst containing the phase change material 150. Suitablematerials for the crucible 120 include but are not limited to siliconcarbide, graphite, reinforced polymer, clay, porcelain, ceramics, carbonnanotubes, aluminium nitride, aluminium oxide, boron nitride, siliconnitride, steel, copper, mullite, zirconium oxide, ductile iron, castiron, stainless steel, brass, alloys of columbian, tantalum, molybdenum,tungsten and combinations thereof. It will be appreciated by the personskilled in the art that the above lists of materials are not anexhaustive list but merely exemplify types of materials that can beused. In another embodiment, the crucible 120 may be a sealed canister.In this regard, the sealed canister has pillow of argon, nitrogen or anyother non-oxidising gas or vacuum. It will be appreciated that any inertatmosphere may be used.

In one embodiment, the crucible 120 is formed of silicon carbide.Silicon carbide is composed of a crystal lattice of carbon and siliconatoms, and is able to provide structural integrity to the crucible 120.Silicon carbide is relatively inert in that it does not react withacids, alkali materials, or molten salts at temperatures up to 800° C.Further to this, silicon carbide forms a silicon oxide coating at 1200°C. which is able to withstand temperatures up to 1600° C. The cruciblematerial therefore includes silicon oxide in one embodiment. Siliconcarbide also has high thermal conductivity, low thermal expansioncharacteristics and high mechanical strength, and this provides thecrucible 120 with exceptional thermal shock resistant qualities. Itshould be apparent that a crucible 120 made of silicon carbide isresistant to chemical reactions, is suitably strong, and has goodthermal conductivity which assists in heating the phase change material150.

The density of the silicon carbide is suitably between about 1 g/cm³ andabout 4 g/cm³, more suitably between about 1.5 g/cm³ and about 3.5g/cm³, preferably between about 2.5 g/cm³ and about 3.5 g/cm³, andpreferably about 3.1 g/cm³.

The crucible 120 is not particularly limited by shape or size. Thecrucible 120 is an open ended container. In one embodiment, the crucible120 has a smaller diameter at the base and a larger diameter at the top.The crucible 120 can have a cylindrical shape, a prism shape, a coneshape, a pyramid shape, a trapezium shape, a pentagon shape, an ovalshape, a trapezoid, a diamond shape or a triangular shape. In oneembodiment, the crucible 120 has a cylindrical shape. It will beappreciated by the person skilled in the art that the list providedmerely exemplifies the types of shapes that the crucible 120 can beformed into and this shape is not limited to the list provided. Thesmaller diameter at the base and the larger diameter at the top allowthe phase change material 150 to expand in a vertical direction ratherthan in a horizontal direction and against the sides of the crucible120. In another embodiment, the energy storage apparatus 100 comprisesmultiple crucibles 120. In one embodiment, the energy storage apparatussuitably comprises 1 to 9 crucibles, more suitably comprises 3 to 9crucibles, most preferably 3, 4 or 9 crucibles.

The heating element 130 is adjacent the crucible 120. The heatingelement 130 generates heat so that thermal energy is transferred to thecrucible 120 and thus the phase change material 150. This is discussedin more detail hereinafter. The heating element 130 is formed ofmaterial that has a high thermal conductivity value to facilitatethermal energy transfer. As such, suitable materials for the heatingelement 130 include but are not limited to molybdenum, nichorme,kanthal, curpronickel, aluminium oxide, boron nitride, mullite, siliconnitride, silicon carbide, zirconium oxide and combinations thereof. Inone embodiment, the heating element 130 is formed of silicon carbide.

The heating element 130 converts electrical energy to thermal energy sothat the phase change material 150 can store said thermal energy. Theheating element 130 sources the energy required for heating from anysource of electricity, such as wind generated electricity, hydro poweredelectricity, fossil fuel powered generators, photovoltaic devices,geothermal power, grid distributed power, heat engines, nuclear fusion,hydrogen fuel cells, thermocouples, thermopiles, thermionic converters,natural gas, coal and combinations thereof.

The voltage of the heating element 130 is suitably between about 10V andabout 1000V, more suitably between about 20V and about 600V, preferablybetween about 20V and 500V, and most preferably between about 24V andabout 415V.

It will also be appreciated that the heating element 130 can be locatedanywhere within the energy storage apparatus 100 as long as the thermalenergy from the heating element 130 is transferred to the phase changematerial 150. However, it is more efficient to have the heating element130 located close to the crucible 120. It will also be appreciated thatthe energy storage apparatus 100 may comprise multiple heating elements130 to ensure that there is sufficient thermal energy transfer to thephase change material 150.

One of the problems associated with thermal energy storage is that thetemperature typically increases with the amount of energy stored withina material. One method of addressing this problem is to utilize agreater mass of material, however, as previously mentioned, there aredisadvantages associated with using a greater amount of phase changematerial, such as storage issues and difficulty in transport. In orderto address this problem the material is heated to higher temperatures tostore greater amounts of energy. However, a material which is muchhotter than the surrounding environment will lose thermal energy to thesurrounding environment much faster compared to a material at a lowertemperature. As such, these high temperatures result in an unacceptableloss of energy.

Phase change material 150 can be used to store larger amounts of thermalenergy without a proportionate increase in temperature, and thereforealleviates the problem associated with the loss of thermal energy to thesurroundings. This is known as latent heat storage.

The principle of latent heat storage is that when heat is applied to aphase change material 150 it changes phase from a solid to a liquid, ora liquid to a gas, by storing the heat as latent heat of fusion orvapourization. When the stored thermal energy is retrieved from thephase change material 150 then it reverts from a liquid to a solid, or avapour to a liquid. Heat storage through phase change has the advantageof compactness because the latent heat of fusion is generally largerthan the enthalpy change for a change in temperature. For example, theratio of latent heat to specific heat of water is about 80 which meansthat the energy required to melt 1 kg of ice is about 80 times themagnitude of the energy required to increase the temperature of 1 kg ofwater by 1° C. It should be clear that there is a significant increasein energy stored within the phase change material 150 when the materialchanges phases and this is not accompanied by a proportionate increasein temperature. This alleviates the problem of loss of thermal energythrough convection, conduction and radiation. Further to this, many ofthe phase change materials known in the art are corrosive, expensive andhave poor thermal conductivity requiring large heat exchange areas.

In order to address the disadvantages associated with using prior artphase change materials, the phase change material 150 should have a highheat storage density for a small temperature variation during the chargeand discharge process. Further to this, the phase change material 150should also have high thermal conductivity and no phase segregation.

The phase change material 150 has a phase change temperature suitablygreater than about 100° C., more suitably between about 200° C. andabout 800° C., preferably between about 400° C. and about 600° C., morepreferably between about 500° C. and about 600° C., and most preferablyabout 576° C.

The phase change material 150 has a specific heat for the liquid statesuitably greater than about 1.1 kJ/KgK, more suitably between about 1.1kG/KgK and about 8 kJ/KgK, preferably between about 1.2 kJ/KgK and about4 kJ/KgK, more preferably between about 1.5 kJ/KgK and about 2 kJ/KgKand most preferably about 1.741 kJ/KgK.

The phase change material 150 has a specific heat for the solid statesuitably greater than about 1 kJ/KgK, more suitably between about 1kG/KgK and about 8 kJ/KgK, preferably between about 1 kJ/KgK and about 4kJ/KgK, more preferably between about 1 kJ/KgK and about 2 kJ/KgK andmost preferably about 1.038 kJ/KgK.

The phase change material 150 has a heat of fusion suitably greater than100 kJ/kg, more suitably between about 100 kJ/kg and about 1000 kJ/kg,preferably between about 300 kJ/kg and 700 kJ/kg, more preferablybetween about 450 kJ/kg and about 600 kJ/kg, and most preferably about560 kJ/kg.

In one embodiment, the phase change material 150 is selected fromaluminium-silicon alloys, aluminium, magnesium chloride, sodium chlorideand potassium chloride. More suitably, the phase change material 150 isselected from the group consisting of aluminium-silicon alloys andaluminium. Preferably, the phase change material is an aluminium-siliconalloy. It will be appreciated that the list of phase change materials150 is not an exhaustive list and merely exemplify certain examples ofthe phase change material 150. The person skilled in the art willappreciate that the phase change material 150 may be other materials notexpressly listed.

The aluminium-silicon alloy comprises suitably between about 1% andabout 50% by weight of aluminium, more suitably between about 5% andabout 25% by weight of aluminium, preferably between about 10% and about20% by weight of aluminium, and most preferably about 12% by weight ofaluminium with the rest of the aluminium-silicon alloy being made up ofsilicon.

An aluminium-silicon alloy comprising about 20% by weight of aluminiumis known as AlSi₂₀, and an aluminium-silicon alloy comprising about 12%by weight of aluminium is known as AlSi₁₂. It will be appreciated thatthe major constituents of the aluminium-silicon alloys are aluminium andsilicon, however, additional elements such as iron, copper, manganese,magnesium, lead, nickel, zinc titanium, tin, strontium, chromium and thelike may be present as impurities. In one embodiment, the phase changematerial 150 is AlSi₂₀. In another embodiment, the phase change material150 is AlSi₁₂.

AlSi₁₂ has a melting temperature of about 576° C. and a heat of fusionof about 560 kJ/kg, and AlSi₂₀ has a melting temperature of about 585°C. and a heat of fusion of about 460 kJ/kg. Table 1 shows the physicalproperties of AlSi₁₂, and it should be clear that the heat of fusion ofAlSi₁₂ is many magnitudes greater than the specific heat capacity ofAlSi₁₂.

TABLE 1 Thermal Physical Properties of AlSi₁₂ Properties of AlSi₁₂Specific heat for solid state, kJ/kgK 1.038 Specific heat for liquidstate, kJ/kgK 1.741 Phase change temperature, ° C. 576 Heat of fusion,kJ/kg 560 Density, kg/m³ 2700 Thermal conductivity, W/M ° C. 160

FIG. 3 shows a graphical representation of the storage capacity per unitmass of AlSi₁₂ versus temperature. The graphical representation showsthat there is a significant increase in the heat storage capacity ofAlSi₁₂ at about 576° C. and this correlates to the phase changetemperature.

It is advantageous if the phase change material 150 changes from a solidto a liquid as there is no significant expansion in the volume of thephase change material 150. Although phase change materials 150 thatchange from a liquid to gas are capable to storing thermal energy, thisphase change results in an increase in volume and pressure. In apreferred embodiment, the phase change in the phase change material 150is from a solid to a liquid when heated.

The heating element 130 generates thermal energy which is transferredthrough the adjacent crucible 120 to the phase change material 150 tostore this energy. It should be apparent to the person skilled in theart that the heating element 130 needs to be placed sufficiently closeto the crucible 120 so that thermal energy can be transferred to thecrucible 120. Additionally, a thermal interface 160 can be utilized inthe volume between the casing 110 and the crucible 120 to facilitatethermal energy transfer.

The thermal interface 160 facilitates the transfer of thermal energyfrom the heating elements 130 to the crucible 120, and also the transferof thermal energy from the crucible 120 to the heat conduit 140. It willbe appreciated that the thermal interface 160 is preferably between theheating elements 130 and the crucible 120. It was also be appreciatedthat the thermal interface 160 is preferably between the heat conduits140 and crucible 120. The thermal interface 160 has high thermalconductivity properties whilst also creating a barrier between thecasing 110 and the crucible 120. This barrier assists in alleviating theproblem of corrosion between the phase change material 150 and thecasing 110.

The thermal interface 160 surrounds the crucible 120, the heatingelement 130, and the heat conduit 140 so that thermal energy can beabsorbed by the crucible 120 and recollected by the heat conduit 140.

In one embodiment, the thermal interface 160 is selected from the groupconsisting of graphite, graphene and carbon nanotubes. In a preferredembodiment, the thermal interface 160 is graphite. Graphite is anexcellent medium to achieve high thermal conductivity between thecrucible 120, the heating elements 130 and the heat conduit 140.Graphite can be found in many forms such as crystalline graphite,amorphous graphite, lump or vein graphite, and pyrolytic graphite.Further to this, graphite has a melting point above 3000° C., whichmakes it compatible with the energy storage apparatus 100.

The volume between the casing 110 and the crucible 120 may be filledwith granular or flakes of graphite, or may be a solid block. Thegraphite block can have the heat conduit 140 and heating element 130embedded at the time of casting the energy storage apparatus 100. Thegraphite can be coated with a carbon nanotube solution. Carbon nanotubesare extremely strong, robust and are very good thermal conductors makingthem suitable as the thermal interface 160 either alone or inconjunction with another material.

To alleviate the problem of thermal energy loss to the surroundings, theenergy storage apparatus 100 may further comprise insulation 170. Theinsulation 170 can suitably be located between the thermal interface 160and the casing 110 to minimize the amount of thermal energy lost to thesurroundings. Further to this, the insulation 170 ensures that thecasing 110 does not get hot and alleviates the problem of an operatorburning themselves if they accidentally come into contact with thecasing 110. As such, it will be appreciated that the insulation 170 willgenerally be located next to casing 110. It will be appreciated thatthere can be multiple layers of insulation 170 using differentmaterials. Suitable materials for these insulation layers includethermal insulation boards, thermal insulation blanks, fiberglass,mineral wool, polymers, and foams. For instance, multiple layers ofCarbolane blankets and boards, of different specifications, can be usedto prevent thermal energy loss. It will also be appreciated that anyinsulation that is able to accommodate the high temperatures can be usedin the energy storage apparatus 100. It will be appreciated that theenergy storage apparatus 100 depicted in FIG. 1 has four layers ofinsulation, however, for convenience these four layers have beenlabelled as insulation 170.

The heat conduit 140 is located adjacent the crucible 120 so that it cancollect the thermal energy from the phase change material 150. The heatconduit 140 can be a high pressure pipe network which facilitatescollection of the stored thermal energy from the phase change material150 and converting said thermal energy to electricity. The heat conduit140 has an inlet and an outlet. The inlet of the heat conduit 140 isgenerally connected to a high pressure pump and the outlet willgenerally be connected to a turbine. In this regard, the heat conduit140 has an inlet where a liquid can be added. As the liquid travelsthrough the heat conduit 140 it is converted to a gas, by absorbing thethermal energy from the phase change material 150, which in turn rotatesa turbine at the outlet to covert the thermal energy to electricalenergy.

The turbine is well known in the art, and those skilled in the art willappreciate that any turbine or device that can produce electricity frommoving gas or liquid can be used with this energy storage apparatus.

The high pressure and high temperature gas passing through the turbinemay be condensed and the residual/waste heat from the hot liquid can beused for co-generation and tri-generation to achieve higherefficiencies.

The heat conduit 140 has a high thermal conductivity value to facilitatethe transfer of heat from the phase change material 150 to the liquid.The heat conduit 140 is suitably made of steel, copper, aluminium oxide,boron nitride, mullite, silicon nitride, silicon carbide, zirconiumoxide, ductile iron, cast iron, stainless steel, brass, alloys ofcolumbian, tantalum, molybdenum, tungsten or combinations thereof. Itwill be appreciated that the above list of materials is not anexhaustive list but merely a list that exemplifies types of materialsthat can be used.

The heat conduit 140 can suitable run along the sides of the crucible tocollected the stored thermal energy. Alternatively, the heat conduit 140can circle around the crucible to ensure efficient transfer of thermalenergy from the crucible 120. It will be clear to the person skilled inthe art that different designs can be used to efficiently transfer heatfrom the heating elements 130 to the crucible 120, and from the crucible120 to the heat conduit 140.

The liquid used in the heat conduit 140 is suitably water. Additivessuch as ethylene glycol, diethylene glycol, propylene glycols, betain,hexamine, phenylenediamene, dimethylethanolamine, sulphur hexafluoride,benzotriazole, zinc dithiophosphates, nanoparticles, polyalkyleneglycols or combinations thereof can be added to inhibit corrosion, alterthe viscosity and enhance thermal capacity.

Referring to FIG. 1a there is shown a cross-sectional view of anotherembodiment of the energy storage apparatus 100. For convenience, thenumbering of the casing 110, the crucible 120, heating element 130, heatconduit 140, phase change material 150, thermal interface 160 andinsulator 170 have been maintained as per FIG. 1. The Applicant submitsthat these features are as described herein for FIG. 1.

This embodiment of the energy storage apparatus 100 comprises multiplecrucibles 120, a heat conduit 140, multiple heating elements 130,multiple layers of thermal interface 160 and insulation 170. In oneembodiment, the energy storage apparatus 100 comprises three crucibles120. It will be appreciated that in between the three crucibles 120 arelocated heating elements 130, a heat conduit 140 and a thermal interface160 to, as mentioned hereinabove, facilitate thermal energy transferfrom the crucible (and the phase change material 150 therein) with theheating elements 130 and heat conduit 140. In one embodiment, the energystorage apparatus 100 comprises four heating elements. Additionally,heating elements 130 are also located on the outer side of the outercrucibles 120. These heating elements 130 are adjacent the outer side ofthe crucibles 120 to further supplement heat transfer to the crucible120, and thus the phase change material 150 therein. In one embodiment,the heating elements are arranged in between the crucibles. In oneembodiment, the heating elements 130 and heat conduit(s) are locatedsubstantially in between the crucibles 120.

During operation of this energy storage apparatus, the heating elements130 provide thermal energy to the crucible 120 (and the phase changematerial 150 therein) through the thermal interface 160 such that thephase change material 150 stores the thermal energy (discussedhereinabove). The thermal energy collected by the phase change material150 can then be reconverted to electrical energy by passing a liquidthrough the heat conduit 140, which absorbs thermal energy from thephase change material 150 and the crucible 120. The liquid is thenconverted to a gas which can then be passed through a turbine (notshown) to generate electricity. It will be appreciated that thisembodiment is efficient as the heating conduit 140 can absorb thermalenergy from multiple crucibles 120 and phase change materials 150, andthis is particularly useful in making the energy storage apparatussmaller and more efficient. In one embodiment, the heat conduits arearranged in between the crucibles.

Additionally, this embodiment also allows for efficient transfer ofthermal energy to the phase change material 150 by use of multipleheating elements 130 located adjacent the crucibles 120. As previouslymentioned, the heating element 130 is formed of a material that has ahigh thermal conductivity value, and as such facilitates thermal energytransfer from the crucible 120 and the phase change material 150 to theheat conduit 140. Finally, there is a layer of insulation 270 on theouter side of the outermost heating elements 130 to ensure that thecasing 110 does not get hot and alleviates the problem of an operatorburning themselves.

It will be appreciated that the above embodiment only exemplifies oneenergy storage apparatus 100 that comprises multiple crucibles andmultiple heating elements. It will be appreciated by the person skilledin the art that the energy storage apparatus 100 may include additionalcrucibles, heating elements, heat conduits, and layers of thermalinterface to provide an energy storage apparatus that has higher energystorage ability. The person skilled in the art will appreciate that thelayout of the apparatus may also be changed so that there is efficienttransfer of thermal energy from the heating elements to the cruciblesand from the crucibles to the heat conduits.

Referring to FIG. 2 there is shown a perspective sectional view ofenergy storage apparatus 200. To clearly depict the energy storageapparatus 200, FIG. 2 does not depict the phase change material or thethermal interface, and only depicts casing 210, crucible 220, heatingelement 230, heat conduit 240 and insulation 270. The casing 210, thecrucible 220, the heating element 230, the heat conduit 240 and theinsulation 270 are as substantially described as the casing 110, thecrucible 120, the heating element 130, the heat conduit 140 and theinsulation 170 described hereinabove. The energy storage apparatus 200depicted in FIG. 2 has three layers of insulation, however, forconvenience these three layers have been labelled as insulation 270.

Referring to FIG. 2a there is shown a perspective section view ofanother embodiment of the energy storage apparatus 220. To clearlydepict the energy storage apparatus 200, FIG. 2a does not depict thephase change material. In this embodiment, the crucibles 220 arearranged in an array in a block of thermal interface 260. The crucibles220 can be inserted into the thermal interface 260 such that they have asnug fit which allows for efficient thermal energy transfer. Also withinthe thermal interface 260 are located heating elements 230 which aresubstantially in between the crucibles 220. The heating elements 230 mayalso be inserted into preformed holes in the thermal interface 260.Additional heating elements 230 are located adjacent the thermalinterface 260. These heating elements 230 provide thermal energy to thecrucibles 220 through thermal interface 260. Multiple heat conduits 240are located in the thermal interface 260 adjacent and in between thecrucibles 220. This embodiment allows for multiple crucibles 220 toabsorb thermal energy from the heating elements 230, whilst alsoallowing multiple heating conduits 240 to absorb thermal energy from thecrucibles when reconverting the thermal energy to electricity. In oneembodiment, the heating elements 230 are located adjacent, or within,the thermal interface 260.

The outer heating elements 230 are surrounded by insulation 270 toensure that the casing 210 does not get hot for the reasons presentedhereinabove. In one embodiment, the energy storage apparatus 200comprises an array of crucibles 220. The array may be in the form of a3×3 array. It will be appreciated that any array can be used with thepresent invention. The array of crucibles 220 may be placed or formed inthe thermal interface 260. In this regard, the crucibles 220 may beinserted into preformed holes in the thermal interface 260. In anotherembodiment, at least a portion of the heating elements 230 are formed inthe thermal interface 260. In yet another embodiment, at least a portionof the heating elements 230 are inserted into preformed holes in thethermal interface 260. In an embodiment, the heat conduits 240 arelocated within the thermal interface 260 and adjacent the crucibles 220.In yet another embodiment, the heat conduits 240 are inserted intopreformed holes in the thermal interface 260.

In one embodiment, the thermal interface 260 is present as a solidblock. The thermal interface 260 may include preformed holes in whichthe crucible 220, heating elements 230 and heating conduit 240 may beformed or inserted. The thermal interface 260 may have a preformed arrayof holes for crucibles 220 to be inserted.

Referring to FIG. 2b is shown the crucible 220 in a perspectivesectional view of the crucible 220 and its positioning in the thermalinterface 260. To clearly depict the energy storage apparatus 200, FIG.2a does not depict the phase change material.

In a second aspect, the invention resides in a method of storing andretrieving energy comprising the steps of:

-   -   a. providing an energy storage apparatus comprising:

a casing

at least one crucible;

at least one heating element adjacent the crucible;

at least one heat conduit, having an inlet and outlet, adjacent thecrucible; and

a phase change material located within the at least one crucible, thephase change material selected from the group consisting ofaluminium-silicon alloys, aluminium, magnesium chloride, sodium chlorideand potassium chloride;

-   -   b. heating the at least one heating element to cause a phase        change in the phase change material, to thereby store energy;    -   c. introducing a liquid to the at least one heat conduit; and    -   d. converting the liquid to a gas through absorption of thermal        energy stored in the phase change material;        -   to thereby retrieve stored energy.

The energy storage apparatus is as substantially described in the firstaspect and hereinabove.

As previously mentioned, electrical energy can be stored in the phasechange material through the collection of thermal energy. The heatingelement converts the electrical energy to thermal energy which istransferred to the crucible and thus the phase change material. As thephase change material is heated it changes phase to store the thermalenergy.

The thermal energy collected by the phase change material is thenreconverted to electrical energy by passing a liquid through the heatconduit. The liquid absorbs the thermal energy from the phase changematerial and is converted to a gas. This high pressure and hightemperature gas is then passed through a turbine to generateelectricity. Therefore, the stored thermal energy in the phase changematerial is retrieved as electricity.

The high pressure and temperature gas can be condensed and theresidual/waste heat from the hot liquid can be used for co-generationand tri-generation to achieve a higher efficiency.

The present energy storage apparatus alleviates the problems of knownstorage systems which suffer from the disadvantage of significantthermal energy loss to the surroundings. The present energy storageapparatus achieves this through the use of a phase change material whichis able to store large amounts of energy without the accompanyingincreasing in temperature. Further to this, the present invention isable to efficiently transfer thermal energy from the heating element tothe crucible, and from the crucible to the heat conduit, through the useof a thermal interface.

The above description of various embodiments of the present invention isprovided for purposes of description to one of ordinary skill in therelated art. It is not intended to be exhaustive or to limit theinvention to a single disclosed embodiment. As mentioned above, numerousalternatives and variations to the present invention will be apparent tothose skilled in the art of the above teaching. Accordingly, while somealternative embodiments have been discussed specifically, otherembodiments will be apparent or relatively easily developed by those ofordinary skill in the art. Accordingly, this invention is intended toembrace all alternatives, modifications and variations of the presentinvention that have been discussed herein, and other embodiments thatfall within the spirit and scope of the above described invention.

1. An energy storage apparatus comprising: a casing; at least onecrucible; at least one heating element adjacent the crucible; at leastone heat conduit, having an inlet and outlet, adjacent the crucible; anda phase change material located within the at least one crucible, thephase change material selected from the group consisting ofaluminium-silicon alloys, aluminium, magnesium chloride, sodium chlorideand potassium chloride.
 2. The energy storage apparatus of claim 1,wherein the phase change material is an aluminium-silicon alloy.
 3. Theenergy storage apparatus of claim 2, wherein the aluminium-silicon alloycomprises between about 1% and about 30% aluminium.
 4. The energystorage apparatus of claim 1, wherein the crucible is selected fromsilicon carbide, graphite, reinforced polymer, clay, porcelain,ceramics, carbon nanotubes, aluminium nitride, aluminium oxide, boronnitride, silicon nitride, steel, copper, mullite, zirconium oxide,ductile iron, cast iron, stainless steel, brass, alloys of columbian,tantalum, molybdenum, tungsten or a combination thereof.
 5. The energystorage apparatus of claim 1, further comprising a thermal interfacebetween the casing and the crucible.
 6. The energy storage apparatus ofclaim 1, wherein the thermal interface is selected from the groupconsisting of graphite and carbon nanotubes.
 7. The energy storageapparatus of claim 1, further comprising insulation.
 8. The energystorage apparatus of claim 5, wherein the thermal interface is in theform a block comprising preformed holes for insertion of the at leastone crucible, the at least one heating element and the at least one heatconduit.
 9. The energy storage apparatus of claim 1, comprising 1 to 9crucibles.
 10. The energy storage apparatus of claim 1, comprising 9crucibles.
 11. The energy storage apparatus of claim 10, wherein thecrucibles are arranged in a 3×3 array.
 12. The energy storage apparatusof claim 1, wherein the heating elements are arranged in between thecrucibles.
 13. The energy storage apparatus of claim 1, wherein the heatconduits are arranged in between the crucibles.
 14. The energy storageapparatus of claim 7, wherein the insulation is located adjacent thecasing.
 15. The energy storage apparatus of claim 5, wherein the thermalinterface is between the heating elements and the crucible.
 16. Theenergy storage apparatus of claim 5, wherein the thermal interface isbetween the heat conduits and the crucible.
 17. A method of storing andretrieving energy comprising the steps of: a. providing an energystorage apparatus comprising: a casing; at least one crucible; at leastone heating element adjacent the crucible; at least one heat conduit,having an inlet and outlet, adjacent the crucible; and a phase changematerial located within the at least one crucible, the phase changematerial selected from the group consisting of aluminium-silicon alloys,aluminium, magnesium chloride, sodium chloride and potassium chloride;b. heating the at least one heating element to cause a phase change inthe phase change material, to thereby store energy; c. introducing aliquid to the at least one heat conduit; and d. converting the liquid toa gas through absorption of thermal energy stored in the phase changematerial; to thereby retrieve stored energy.